Interleaved power factor correction techniques are being used, primarily, to reduce conduction losses in connection with power factor correction (PFC) pre-regulators and to increase power densities by reducing total inductor magnetic volume. Interleaving PFC pre-regulators, in which two or more PFC pre-regulators are operated out-of-phase, is commonly employed in applications such as—for the purpose of illustration and not limitation—power supplies for personal computers, computer server power supplies, and in industrial AC to DC power conversion.
Efficiency improvements using interleaved techniques, however, are only observed at higher power levels where conduction losses dominate over switching losses. However, this technique increases parasitic switch/field-effect transistor (FET) capacitance, which increases switching losses and reduces light load efficiency.
For example, referring to FIG. 1, a typical AC to DC converter 10 with interleaved PFC pre-regulators includes a first stage (Stage 1) structured and arranged to provide interleaved PFC AC to DC conversion and a second stage (Stage 2) structured and arranged to provide DC to DC conversion. The first stage includes a first PFC pre-regulator 12 (Phase 1) and at least one additional PFC pre-regulator 14 (Phase 2) that are interleaved. The number of additional pre-regulator 14 is related to the number of desired phases. Hence, a two phase system (as shown in FIG. 1) will have a first PFC pre-regulator 12 (Phase 1) interleaved with a second PFC pre-regulator 14 (Phase 2); while and a three phase system (not shown) will have a first PFC pre-regulator 12 interleaved with a second PFC pre-regulator 14 and with a third PFC pre-regulator (not shown).
The interleaved PFC pre-regulators 12 and 14 are adapted to provide AC to DC power conversion. Each of the interleaved pre-regulators 12 and 14 is structured and arranged to include an inductive element L1 and L2 and a current blocking device, such as diode D1 and D2. Those of ordinary skill in the art can appreciate that other means of blocking current besides diodes can be used.
In pertinent part, each of the interleaved PFC pre-regulators 12 and 14 further includes a switching device 13 and 30, which is shown as field effect transistors (FETs) Q1 and Q2, and a gate driving device 11 and 28. The gate driving devices 11 and 28 are adapted for opening, i.e., turning OFF, and closing, i.e., turning ON, the corresponding gates of the switching devices 13 and 30. Those of ordinary skill in the art can appreciate that other switching device types can also be used.
The front end (AC to DC conversion) stage (Stage 1) of the power converter 10 is generally followed by a second downstream (DC to DC conversion) stage (Stage 2). The second stage includes a peak current mode controlled step down converter 16, such as a step down converter, a fly-back converter, and the like, that is adapted to step down the regulated boost voltage (VBOOST) to a more usable voltage. The step down converter 16 includes a transformer 19, a current sense resistor 17, and a switching device 15. For simplicity, efficient operation of the step down converter 16 can be controlled using peak current mode control techniques that are known to the art.
A problem with this configuration, however, is that, at lighter power loads, conduction losses are negligible and switching losses dominate. Recalling that, heretofore, interleaving PFC pre-regulators have been used to reduce conduction losses, traditional interleaving of PFC pre-regulators 12 and 14 reduces efficiency at lighter power loads.
To improve efficiency at these lighter power loads and to reduce switching losses, it would be desirable to provide means and methods for selectively turning OFF the second PFC pre-regulator 14 and any other PFC pre-regulators (not shown) during instances of lighter power loads and turning ON or leaving ON the additional PFC pre-regulator(s) 14 during instances of higher power loads.